In recent years, pressure type flow control apparatus have been increasingly used in gas supply facilities in semiconductor manufacturing, chemical products-related facilities, and the like, replacing thermal type flow control apparatus. The simple structure of a pressure type flow control apparatus makes it possible to reduce production costs and downsize the facilities. Furthermore, a pressure type flow control apparatus rivals, or exceeds, a thermal type flow control apparatus both in accuracy and responsiveness.
In these gas supply facilities, it is a common practice to regularly inspect devices and valves to see the operational conditions. Inspection activities on gas supply facilities thus is indispensable for the stable supply of a gas from gas supply facilities.
In response to such a demand as described above, applicants of the present invention have developed a method for detecting the malfunction of a valve while gas is supplied using a pressure type flow control apparatus as shown in FIG. 9, and disclosed the method in Japanese Patent Application No. 2005-253996. In particular, techniques in the aforementioned Japanese Patent Application No. 2005-253996 have made it possible to check operational conditions of valves V1, V2, V3, and to check for the existence of sheet leaks (hereinafter called a “check”), within a gas supply facility. As shown in FIG. 9, the valves V1, V2, V3 are checked without removal from pipe passages, thus achieving excellent practical effects. In accordance with FIG. 9, Go designates a purge gas, Gp designates a process gas, FCS (flow control system) designates a pressure type flow control apparatus, 1a, 1b, 1c designate pipe passages, and E designates a process chamber.
In accordance with the gas supply facility shown in FIG. 9, in order to determine whether valves V1, V2, V3 are operating normally or not (i.e., being open or closed), checks are conducted by following the steps shown in FIG. 10.
First, the malfunction check starts with Step So. Then, at Step S1, valve V1 is closed, valve V2 is switched from “open” to “closed”, and valve V3 is closed. After these operations, a pipe passage 1b on the downstream side of the FCS is filled with N2. Next, at Step S2, the displayed pressure P1 of the FCS is checked to see if the increase/decrease ΔP1 of the pressure P1 is zero or not. In the case that ΔP1 is not zero and P1 goes up, it is determined that there is an abnormal condition with either valve V1 or valve V2, or both valves V1 and V2 (i.e., either sheet leaks or operational irregularity is present). And, in the case that P1 goes down, it is determined that V3 is abnormal (i.e., sheet leaks or operational irregularity are present) (Step S3).
Next, at Step S4, a process gas (i.e., a use gas) Gp is flowed into the FCS by making valve V1 open and valve V2 close, and the displayed pressure P1 of the FCS is checked at Step S5. In the case when a rise of P1 is observed, it is determined that V1 is functioning normally (Step S7); on the other hand, in the case that there is no rise of P1, it is determined that valve V1 is malfunctioning (Step S6), thus the operational conditions of V1 are confirmed. Then, after V1 is closed and V2 is opened at Step S8, the displayed pressure P1 of the FCS is checked (Step S9). In the case when there is no rise of P1, it is determined that valve V2 is malfunctioning (Step S10), thus the operational conditions of valve V2 are confirmed. On the other hand, when a rise of P1 is observed, it is determined that valve V2 is functioning normally (Step S11).
Then, at Step S12, it is determined whether or not the malfunction of valves found at the Step S2 is applicable to the operational malfunction of a valve V3. Specifically, if the result of Step S2 is “NO” (that is, one of valves V1, V2, V3 is malfunctioning), and valves V1 and V2 are functioning normally, it is determined that a valve V3 is malfunctioning (Step S13). If the result of Step S2 is “YES”, then, it is determined that all the valves V1, V2, V3 are functioning normally (Step S14).
After it is determined that the aforementioned valves V1, V2, V3 are all operating normally, sheet leaks are then checked at Step S15. To determine whether the operational conditions of the valves are normal or not, there exist prerequisites that    (a) there should be no outside leaks (i.e., leaks from joints, bonnets, and the like) with valves V1, V2, V3, FCS, pipe passages 1a, 1b, 1c, and the like, except sheet leaks,    (b) driving parts of all valves are under normal operation,    (c) the FCS is functioning normally, and    (d) V1 and V2 are not simultaneously released.
However, as shown in FIG. 11, the system is constituted so that, with a pressure type flow control apparatus FCS, a flow rate of a gas passing through a throttle mechanism is computed on the basis of the gas pressure P1 and gas temperature T1 on the upstream side of a throttle mechanism 8 such as an orifice, a sonic nozzle, or the like, (Japanese Unexamined Patent Application Publication No. 8-338546 and others). Therefore, for example, even when valve V3 on the downstream side of the throttle mechanism is closed, and the flow rate of a gas passing through throttle mechanism 8 is found to be zero, a gas flow rate Qf is computed by flow rate computation apparatus 20 of flow rate computation circuit 13 if gas pressure P1 is applied to pipe passage 3, thus what is computed is outputted as a flow rate output signal Qo. Specifically, even when there occurs no gas flow due to the malfunction of releasing valve V3, a flow rate output signal Go is outputted to the outside. In FIG. 11, 2 designates a control valve, 12 designates a flow rate output circuit, 14 designates a flow rate setting circuit, 16 designates a computation control circuit, 21 designates a comparison circuit, and Qy designates a control signal (Qy=Qe−Qf).
When opening/closing operations of the valve V3 on the downstream side of the FCS are conducted while the gas supply facility is at work, there is no way to find out directly if a malfunction of the releasing operations of the valve V3 exists or not.
The reason for this is, as described above, that even when a flow rate of gas passing through throttle mechanism 8 is found to be zero (valve V3 is in the state of closure), a flow rate output signal Qo is outputted to the outside if there exists pressure P1 on the upstream side of throttle mechanism 8. In other words, it is assumed that valve V3 is kept open all the time from the viewpoint of a flow rate output signal Qo even when valve V3 actually remains closed due to malfunction of valve V3.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 8-338546
Patent Document 2: Japanese Unexamined Patent Application Publication No. 2000-66732